Field of the Invention
The present invention relates to a foldable display device, and more particularly to a foldable display device that is capable of increasing the support force of a display panel in the vertical direction and minimizing the stress applied to a folding part when folded.
Discussion of the Related Art
Image display devices are a core technology in the information and communication age for displaying various kinds of information on a screen. Image display devices have been developed such that they are thinner, lighter, and portable and exhibit high performance. Organic light-emitting display devices control the amount of light that is emitted from an organic light-emitting layer to display an image. Organic light-emitting display devices have been highlighted as flat panel display devices, which are lighter and smaller than cathode ray tubes (CRT).
In an organic light-emitting display device, a plurality of pixels are arranged in the form of a matrix to display images. Each pixel includes a light-emitting device, and the organic light-emitting display device includes a pixel drive circuit including a plurality of transistors configured to independently drive the respective light-emitting device of each pixel.
Using a self-emitting organic light-emitting device, an organic light-emitting display device does not need an additional light source, and may be realized as an ultra-thin display device. In recent years, therefore, research has been actively conducted into an in-cell touch type foldable display device, which uses an organic light-emitting device and includes a touch electrode array in a light-emitting cell.
A foldable display device has a structure in which the display device itself, including a display panel, is foldable. In order to protect such a flexible display panel, a middle frame is provided. The middle frame, which is provided at the lower surface of the display panel to protect the display panel, must be designed to be foldable.
In a conventional foldable display device, the region of a middle frame corresponding to the folding part has a soft structure including silicone resin, and the remaining region of the middle frame corresponding to a non-folding part is made of metal or rigid plastic to protect the display panel.
In the conventional foldable display device using the middle frame, the folding part and the non-folding part are formed of different materials. The materials are different from each other in terms of their physical properties, such as rigidity, elasticity, and softness. In addition, the material is compressed differently during the processing. As a result, there is a high possibility of irregularities being formed at the interface between the different materials. When the irregularities are formed between the folding part and the non-folding part, a display screen may become transferred or distorted. In addition, when the conventional foldable display device using the middle frame is folded multiple times, the soft folding part is stressed, with the result that the display panel may swell or sag. Furthermore, the soft folding part may be deformed or hardened under high-temperature, high-humidity conditions.